We are at the dawn of a new era of quantitative consumer exposure and risk assessment of chemicals driven by regulatory mandates. This remarkable development also signals the beginning of a dramatic resurgence in the need for and development of human exposure models. This paper presents some of the philosophical background underlying exposure modeling in the context of human health risk assessment. The basic types of and structure of inhalation exposure models are discussed, as well as the research needed to move us forward into this exciting new period of development.